Commercial cell therapy products are preferably produced in aseptic systems that are closed. However, the growth of many cell types used for commercial cell therapy product is anchorage-dependent.
While stirred tank reactors, shaker flasks, spinner flasks, uplift reactors, and the like, are all useful for cells that grow in suspension (e.g. hybridomas for monoclonal antibody production, many cells used for recombinant DNA technology, and most insect cell cultures), the options for growing and expanding anchorage-dependent cells are more limited.
Included among the anchorage-dependent cells are many normal diploid cell strains, as well as most primary cell types. Options for large-scale production of such cells include roller bottles, fiber beds, hollow fiber systems, multi-plate or stacked-plate culture systems, cell cubes, and microcarriers, each of which has advantages and disadvantages.
Microcarrier-based methods of cell culture provide many advantages including ease of downstream processing in many applications. Microcarriers are typically roughly spherical in shape, and can be either macro- or micro-porous, or solid. The use of microcarriers for cell attachment facilitates the use of stirred tank and related reactors for growth of anchorage-dependent cells. The cells attach to the readily suspended microparticles. The requirement for suspendability limits the physical parameters of the microcarriers themselves. Thus, microcarriers commonly have a mean diameter in the range of 50-2000 microns. In some applications solid-type microcarriers range from about 100 to about 250 microns whereas porous-type microcarrier beads range from about 250 to about 2500 microns. These size ranges allow for selection of microcarriers which are large enough to accommodate many anchorage-dependent cells, while small enough to form suspensions with properties suitable for use in stirred reactors.
Both porous and solid types of microparticulate carriers are commercially available from suppliers. Examples of commercially available microcarriers include Cytodex® 1 and Cytodex® 3, which are both dextran-based microcarriers from GE Healthcare Life Sciences. Porous microcarriers on the market include CYTOLINE as well as Cytopore® products also from GE Healthcare Life Sciences. Biosilon® (NUNC) and Cultispher® (Percell Biolytica) are also commercially available.
Although for some types of cells, the morphology of cells grown on highly curved surfaces, such as those provided by microcarriers, can be an issue, generally microcarriers provide many advantages in terms of large-scale growth including ease of harvesting cells, and ease of separating useful extracellular products from the cells themselves. A need exists in the art for an efficient and high yield method to grow and harvest anchorage dependent cells such as postpartum cells derived from umbilical cord or placenta.